Studies by Spiegel, et al. (16) and others (2, 10, 14, 15) have suggested that there may exist a correlation between the presence of specific species of black pimented Bacteroides (BPB) in the periodontal pockets and the severity of periodontal disease. Utilizing this information, we propose to: 1) clinically evaluate gingival sites of normal and periodontally involved patients, 2) collect sub-gingival plaque samples from these sites and examine them for the presence of specific species of BPB, using standard microbiological procedures, 3) correlate the extent of disease at the sample site with the presence or absence of specific species of BPB, 4) develop an indirect sandwich enzyme-linked immunosorbent assay for detecting antigens specific for Bacteroides species in these subgingival plaque samples, and 5) correlate the serological diagnosis of the presence of Bacteroides antigens with cultural studies of the same plaque sample and the clinical measurements of the disease. It is hoped that the above serological laboratory test will prove to be useful as a diagnostic tool in the initial evaluation of the periodontal disease and in the establishment and monitoring of the therapeutic regimens.